We calculate the microlensing event rate and typical time-scales for the free-floating planet ( FFP ) population that is predicted by the core accretion theory of planet formation .
The event rate is found to be \sim 1.8 \times 10 ^ { -3 } of that for the stellar population .
While the stellar microlensing event time-scale peaks at around 20 days , the median time-scale for FFP events ( \sim 0.1 day ) is much shorter .
Our values for the event rate and the median time-scale are significantly smaller than those required to explain the ( ) result , by factors of \sim 13 and \sim 16 , respectively .
The inclusion of planets at wide separations does not change the results significantly .
This discrepancy may be too significant for standard versions of both the core accretion theory and the gravitational instability model to explain satisfactorily .
Therefore , either a modification to the planet formation theory is required , or other explanations to the excess of short-time-scale microlensing events are needed .
Our predictions can be tested by ongoing microlensing experiment such as KMTNet , and by future satellite missions such as WFIRST and Euclid .